To meet the increasing demands for smaller electronic devices, CMOS devices have continuously been scaled down. One problem associated with CMOS scaling involves short channel effects (SCE's). Ultra-thin-body-and-BOX (i.e., UTBB, UT2B, or UTB2) fully depleted SOI devices are an attractive candidate for further CMOS scaling due to their superior SCE control, smaller threshold voltage (Vt) variability, and compatibility with mainstream planar CMOS technology. Compared to conventional ETSOI devices, UTBB improves SCE by further reducing electric field coupling between source and drain with a thinner BOX and ground-plane (GP). By applying appropriate substrate bias and GP doping/polarity, multi-Vt devices can be realized with a simple gate stack. Ground Plane doping of ˜5e18/cm3 is required to achieve desirable Vt modulation and optimum GP resistance. The substrate-bias provides an extra dynamic power capability at the device level.
Doping of the UTBB and Double BOX devices of the instant disclosure can be done by (1) using a thin-BOX SOI wafer with a predoped substrate from the vendor or (2) by implanting ions into an undoped substrate thin-BOX SOI wafer. For technologically relevant BOX thicknesses of 10-25 nanometers, the ion implantion through the SOI layer causes substantial “poisoning” of the SOI channel. This is problematic because the dopant concentration in the thin SOI channel after ion implantation may be ˜5-8e17/cm3, and could lead to increased Vt variability due to random-dopant fluctuations. One way to circumvent this problem is by using a thin-BOX ETSOI substrate with a predoped substrate. However, experiments on such predoped UTBB substrates have shown that the dopant diffuses from the substrate through the thin-BOX and into the SOI channel when exposed to the FEOL thermal budget resulting in punch-through (shorted) devices. Therefore, it would be desirable to fabricate a UTBB device wherein the rate of dopant diffusion into the SOI channel is reduced after FEOL thermal budget for devices utilizing predoped or implanted substrates.